1. Field of the Invention
The invention relates to vehicle steering devices, and more particularly to vehicle steering devices capable of easily detecting a failure of a sensor etc. and capable of continuously steering a vehicle after the failure occurs, failure determination methods for the vehicle steering devices, and steering motor control methods.
2. Description of the Related Art
A device called a steer-by-wire system is proposed as an example of vehicle steering devices.
In this device, a steering operation mechanism is not mechanically coupled to a steering mechanism. This device includes a steering controller that controls a steering motor provided in the steering mechanism according to inputs from various sensors provided in the steering operation mechanism and the steering mechanism. Examples of the sensors provided in the steering operation mechanism include a steering operation angle sensor that detects a steering operation angle of a steering operation unit that is turned by a driver, and a torque sensor that detects steering operation torque applied to the steering operation unit. Examples of the sensors provided in the steering mechanism include a motor angle sensor that detects a rotation angle of the steering motor, and a steered angle sensor that detects a steered angle of steered wheels that are steered by driving of the steering motor.
See, e.g., Japanese Patent Application Publication Nos. H10-197238 (JP H10-197238 A) and 2013-112279 (JP 2013-112279 A).
The steer-by-wire system does not use mechanical coupling between the steering operation mechanism and the steering mechanism to steer a vehicle. Instead, the steer-by-wire system drivingly controls the steering motor by the steering controller according to the inputs from the various sensors, thereby steering a vehicle according to the turning operation of the steering operation unit. It is therefore required to detect failures of the sensors or a failure of a mechanical element that moves according to the rotary motion of the steering motor, etc.